Active noise cancelling (ANC), also known as active noise cancellation, active noise control or active noise reduction (ANR) is often used in headphone applications. ANC is used to suppress noise that is generated by the environment of the user and which might reduce the user's musical enjoyment or generally conflict with a user's desire for silence. For feedback ANC, usually a feedback microphone is arranged close to a loudspeaker. The microphone receives a sum signal including a sound signal radiated by the loudspeaker as well as any unwanted noise from external sources. The loudspeaker may radiate desired sound signals (e.g., music or any other acoustic signal), which may be linearly distorted (e.g., amplitude and phase response alterations), as well as harmonic and nonlinear distortion products and noise. Information about the noise from external sources as well as from the loudspeaker, distortion products from the loudspeaker and any linear distortion that may be applied to a desired sound signal by the loudspeaker, may be obtained by subtracting the desired sound signal from the sum signal. A noise and distortion reducing signal may then be emitted which has the same amplitude but an inverted phase as compared to the noise and distortion signal. By superimposing the noise and distortion signal and the noise and distortion reducing signal, the resulting difference signal between the desired sound signal and the sum signal picked up by the microphone, also known as error signal, ideally tends towards zero. ANC and distortion compensation systems generally perform well for traditional headphones which create a pressure chamber around the ear. However, problems arise in open or semi-open headphones or, generally, in any sound devices which do not form a pressure chamber around the user's ear.